1. Field of the Invention
The invention relates to a medium conveying apparatus.
2. Related Background Art
Hitherto, in an image forming apparatus such as printer, copying apparatus, facsimile apparatus, or the like, as a medium conveying apparatus for conveying a recording medium to an image forming unit, one recording medium is separated from a plurality of recording media stacked and enclosed on a medium tray, fed out, and thereafter, conveyed by conveying rollers as a plurality of conveying units.
To separate one recording medium from the plurality of stacked recording media and feed it out, when a paper feed roller is pressed toward a front edge portion of the top recording medium and the paper feed roller is rotated by a driving force transfer unit having a one-way clutch, the top recording medium is fed out, the front edge of the recording medium passes through the conveying roller arranged on the downstream side from the paper feed roller, and thereafter, the driving of the paper feed roller is stopped.
After the driving of the paper feed roller is stopped, the recording medium which is conveyed by the conveying rollers drives the paper feed roller. When a rear edge of the recording medium passes through the paper feed roller, the paper feed roller is stopped, and the recording medium is separated (for example, refer to JP-A-9-263336).
FIG. 2 is a perspective view showing a main section of the conventional medium conveying apparatus. FIG. 3 is a perspective view showing a main section of another conventional medium conveying apparatus.
In FIG. 2, F denotes a supporting frame and reference numeral 15 denotes a first conveying roller unit rotatably supported to the supporting frame F. The first conveying roller unit 15 comprises a conveying roller 101 and a pinch roller 102. The conveying roller 101 comprises rubber rollers 103 arranged in predetermined positions of a shaft sh1. Reference numeral 16 denotes a second conveying roller unit rotatably supported to the supporting frame F. The second conveying roller unit 16 comprises a conveying roller 104 and a pinch roller 105. A recording medium (not shown) is supplied to the first conveying roller unit 15 in the direction shown by an arrow A, ejected from the first conveying roller unit 15, thereafter, guided by a curved guide 108, supplied to the second conveying roller unit 16, and ejected from the second conveying roller unit 16 in the direction shown by an arrow B.
Although a paper feed roller (not shown) is arranged on the upstream side from the first conveying roller unit 15 in the conveying direction of the recording medium, as mentioned above, when the rotation of the paper feed roller is stopped, the first conveying roller unit 15 needs to solely convey the recording medium in the state where loads of the paper feed roller and other devices have been applied.
As shown in FIG. 2, however, since the rubber roller 103 is small, a conveying force of the recording medium cannot be increased in the conveying roller 101. Therefore, as shown in FIG. 3, a rubber roller 113 is enlarged so as to sufficiently assure an area touch the recording medium, thereby increasing the conveying force of the recording medium.
However, in the conventional medium conveying apparatus, since an amount of rubber material which is used is increased by an enlargement amount of the rubber roller 113, costs rise.